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Date of Final Oral Examination (Defense)
Type of Culminating Activity
Thesis - Boise State University Access Only
Master of Science in Materials Science and Engineering
Materials Science and Engineering
Lan Li, Ph.D.
Mike Hurley, Ph.D.
Yue Chen, Ph.D.
This thesis documents the first-principles computational modeling of surface interactions between water molecules, chlorine ions and the S-Al2CuMg and θ-Al2Cu secondary phases of the 2XXX series of aluminum alloys by analyzing data obtained from electronic, structural and topological properties. Information on the fundamental initiation of surface processes when reacting to aforementioned species remains still unknown. This thesis can accelerate materials development for the mitigation of localized corrosion, such as pitting corrosion, by providing insight into the structure-property relationships of surfaces and adsorbates. Aluminum forms a thermodynamically stable oxide layer that prevents corrosion. In certain conditions or with damage of the oxide layer, localized corrosion processes may occur. Alloying is a common technique used for improving mechanical properties, but the typically corrosion resistance is simultaneously decreased. S-Al2CuMg and θ-Al2Cu are two common aluminum-based secondary phases that when precipitated serve as a strengthening mechanisms of Al-based alloys. These microstructure features also provide preferential initiation points for localized corrosion. This work aims at using density functional theory (DFT)-based approaches to reveal the origins of localized corrosion processes. The approaches consist of electronic local density of states (LDOS), electron localization functions (ELFs), energy-resolved partial charge densities, work function and surface energy calculations to assess the stability of each phase. Cl- ions cause atomic distortions on the surface layers. The nature of the distortion could be a factor to weaken the interlayer bonds in the Al2Cu and Al2CuMg secondary phases, facilitating the initiation of corrosion process. Electronic structure calculations revealed both sharing and transferring of electrons in the surface and Cl- ion interactions for both surfaces, suggesting ionic and covalent bonding features. Surface energy calculations indicated that the S-phase Al2CuMg structure has a more active surface than the θ-phase Al2Cu does. The reaction of the surfaces with other species/ions (i.e. Cl- ions) increases surface stability. However, the S-phase naturally displays a more uneven charge density distribution on its surface, causing surface instability and catalyzing the chemical reactions to form various new species and compounds.
da Silva, Thiago Henrique, "First-Principles Surface Studies of Chlorine Ion and Water Molecule Interactions with the Secondary Phases of Aluminum-Copper and Aluminum-Copper-Magnesium Alloys" (2018). Boise State University Theses and Dissertations. 1383.